Precise targeting of tumors, lesions, and anatomical structures with a probe, needle, catheter, or electrode inside the brain based on preoperative CT/MRI images is the standard of care in many keyhole neurosurgical procedures. The procedures include tumor biopsies, treatment of hydrocephalus, aspiration and evacuation of deep brain hematomas, Ommaya catheter insertion, Deep Brain Stimulation, and minimal access craniotomies, among others. In all cases, misplacement of the surgical instrument may result in non-diagnostic tissue or catheter misplacement, as well as hemorrhage and severe neurological complications. These minimally invasive procedures are difficult to perform without the help of support systems that enhance the accuracy and steadiness of the surgical gestures.
All of these procedures have four important common properties:                1) they are minimally invasive surgeries (MIS) performed via a keyhole of 3-30 mm diameter opened on the skull dura;        2) they require precise targeting and mechanical guidance support;        3) the targets and entry points are determined preoperatively in a CT/MRI image; and        4) it is assumed that little or no brain shift occurs due to the MIS approach.        
All such minimally invasive keyhole neurosurgeries follow a similar protocol, both preopertively and intraoperatively, as shown in the following summary:
1. Preoperatively
(a) Pre-imaging preparation: implant skull screws and/or attach skin markers
(b) Image acquisition: acquire a CT/MRI image
(c) Planning: elaborate the preoperative plan: identify targets and entry points
2. Intraoperatively
(a) Preparation: set up the support system and make entry point incision
(b) Localization: locate needle/probe at entry point and adjust orientation
(c) Guidance: provide mechanical guidance for needle/probe insertion
(d) Insertion: insert needle to planned depth at proper speed/force
(e) Repeat steps (a)-(d) as necessary
There are four main types of support systems currently in use in the execution of minimally invasive keyhole neurosurgery:
1. Stereotactic frames;
2. Navigation systems;
3. Robotic systems; and
4. Interventional imaging systems.
Each of these systems has comparative advantages and disadvantages, as generally perceived by those active in the field, with each system having its proponents and opponents. The following is a summary of these systems with a suggested list of the advantages and disadvantages of each:
1. Stereotactic frames, such as those supplied by Radionics Inc., of Burlington, Mass., USA, or as used in the Leksell Gamma Knife® supplied by Elekta AB of Stockholm, Sweden, provide precise positioning with a manually adjustable frame rigidly attached to the patient's skull. Prior to image acquisition, four frame position screws are implanted in the patient's skull. An imaging coordinate box is mounted on the frame and the patient is scanned with it. The surgeon identifies the brain targets and entry points on the images and computes the corresponding stereotactic frame coordinates. Intraoperatively, the stereotactic frame is adjusted according to the computed coordinates and mounted on the immobilized patient skull at the implanted screws. Keyhole surgery of the skull opening is then performed. Optionally, a linear drive needle insertion guide is mounted on the frame to automate needle insertion and retraction. The advantages of stereotactic frames are: 1) introduced in the 1970's, they are the current standard of care and are extensively used and clinically tested; 2) they are relatively accurate (≦2 mm of the target) and provide rigid support and guidance for needle insertion, and; 3) they are relatively inexpensive (USD 50K) as compared to other systems. Their generally perceived disadvantages are: 1) they require the preoperative implantation of the head screws under local anesthesia; 2) they may cause discomfort to the patient before and during surgery; 3) they are bulky, cumbersome, and require manual adjustment during surgery; 5) they require patient head immobilization during surgery; 6) selecting new target points during surgery requires new manual computations for frame coordinates; and 7) they do not provide real-time feedback and validation of the needle position.2. Navigation systems such as those supplied by Medtronic Inc. of Minneapolis, Minn., USA and BrainLAB AG of Heimstetten, Germany, show in real time the location of hand-held tools on the preoperative image onto which targets have been defined. Such systems have been described in US Patent Application Publication No. 2002/0183608, assigned to BrainLAB, in U.S. Pat. Nos. 5,383,454 and 5,891,034 to R. D. Bucholz, and in numerous articles, such as those by Kosugi, Y. et al. “An articulated neurosurgical navigation system using MRI and CT images”, IEEE Trans. on Biomedical Eng. Vol. 35 (2), 1998, pp 147-152; by Akatsuka, Y. et al. “AR navigation system for neurosurgery”, Proc. of Medical Imaging and Computer-Aided Interventions, 2000, pp 833-838; and by Grimson, E, et al., “Clinical experience with a high precision image-guided neurosurgery system”, Proc. of Medical Imaging and Computer-Aided Interventions, 1998, pp 63-72. The registration between the preoperative data and the patient is performed via skin markers affixed to the patient's skull before scanning, or by acquiring points on the patient's face with a laser probe or by direct contact. Augmented with a manually positioned tracked passive arm such as the EasyTaxis™ supplied by Phillips Inc., or the Navigus™ System supplied by Image-Guided Neurologics Inc, and as described in the article by W. A. Hall et al., Navigus trajectory guide, Neurosurgery, 46(2), pp. 502-4, 2000, they also provide mechanical guidance for targeting. Since nearly all navigation systems use optical tracking, careful camera positioning and maintenance of a direct line of sight between the camera and tracked instruments is required at all times. The main advantages of navigation systems are that: 1) they provide continuous, real-time surgical tool location information with respect to the defined target; 2) they allow the selection of new target points during surgery, and; 3) introduced in the 90's, they are gaining wide clinical acceptance. Their generally perceived disadvantages are: 1) their cost, which is of the order of USD 200K; 2) they require head immobilization or compensation for patient head movement by the use of dynamic referencing; 3) they require the maintenance of a line of sight; 4) they require manual passive arm positioning, which can be time-consuming and error-prone; and 5) they require intra-operative registration, whose accuracy depends on the positional stability of the skin.3. Robotic systems provide frameless stereotaxy with a robotic arm that automatically positions itself with respect to a target defined in the preoperative image. Such systems for use in neurosurgery have been described in the articles by Chen, M. D., et al., “A robotics system for stereotactic neurosurgery and its clinical application”, Proc. Conf. Robotics and Automation, 1998, pp 995-1000; by Masamune, K. Ji, et al., “A newly developed stereotactic robot with detachable drive for neurosurgery”, Proc. of Medical Image Computing and Computer Aided Imaging, 1998, pp. 215-222, by Davies, B. et al., “Neurobot: a special-purpose robot for neurosurgery”, Proc. Int. Conf. on Robotics and Automation}, 2000, pp 410-414; by Hang, Q. et al., “The application of the NeuroMate Robot: a quantitative comparison with frameless and frame-based surgical localization systems”, Computer Aided Surgery, Vol. 7 (2), 2002, pp 90-98, and by McBeth, P. B. et al., “Robotics in neurosurgery”, The American Journal of Surgery Vol. 188, pp. 68S-75S, 2004.
They have the potential to address intraoperative localization, guidance, and insertion (steps 2b, 2c, 2d in the summary list above) with a single system. The registration between the preoperative image and the intraoperative situation is done by direct contact or with video or X-ray images. Two floor-standing commercial robots include the NeuroMate™ supplied by Integrated Surgical Systems, USA and PathFinder™, supplied by Armstrong HealthCare Ltd, of the UK. Their advantages are that: 1) they provide a frameless integrated solution; 2) they allow for intraoperative plan adjustment; and 3) they are rigid and accurate. Their generally perceived disadvantages are that: 1) they are bulky and cumbersome due to their size and weight, and thus pose a potential safety risk; 2) they require head immobilization or real-time tracking, 3) they are costly (USD 300-500K), and 4) there are not commonly used, with only approximately a dozen systems currently deployed.
4. Interventional imaging systems produce images showing the actual needle/probe position with respect to the brain anatomy and target. Such systems are described in the articles by Tseng, C-S. et al., “Image guided robotic navigation system for neurosurgery”, Journal of Robotic Systems, Vol. 17, (8), 2000, pp 439-447; by Chinzei, K and Miller. K., “MRI Guided Surgical Robot”, Australian Conf. on Robotics and Automation}, Sydney, 2001; and by Kansy, K. et al. “LOCALITE—a frameless neuronavigation system for interventional magnetic resonance imaging”, Proc. of Medical Image Computing and Computer Assisted Intervention, 2003, pp 832-841.
A few experimental systems also incorporate real-time tracking, such as is supplied by Stereotaxis, Inc., of St. Louis Mo., USA, and robotic positioning devices. The main advantage is that these systems provide real-time, up-to-date images that account for brain shift, and needle bending. Their main generally perceived drawbacks are: 1) limited availability; 2) cumbersome and time-consuming intraoperative image acquisition; 3) high nominal and operational costs, and 4) for intraoperative MRI, complete, expensive room shielding is required.
The comparative characteristics of these four prior art systems are summarized in Table 1, which shows a nominal rating scheme, based on generally accepted perception of the various support techniques for minimally invasive keyhole neurosurgery, though it is to be understood that different practitioners may consider somewhat different ratings for systems which they espouse. In this table, ‘+++’ indicates the most advantageous, and ‘+’ the least advantageous. Furthermore, the column heading abbreviations are for:
1) clinical accuracy, 2) range of applicability, 3) ease of use in the Operating Room, 4) intraoperative adaptability of preoperative plan, 5) bulk, including size and weight, 6) patient morbidity, and 7) system cost.
TABLE 1EaseHeadMethodAccuracyRangeof useAdaptabilityBulkMorbidityfixationCost1.Stereotactic++++++++++yes+++frame2.Navigation++++++++++++yes++3.Robotics+++++++++++yes+4.Interventional++++++++++++no+imaging
To date, few clinical studies have been performed comparing the clinical accuracy of these systems. Frameless navigation has been compared with frame-based stereotaxy in the article by Dorward, N. L. et al., “The advantages of frameless stereotactic biopsy over frame-based biopsy”, British Journal of Neurosurgery, Vol. 16 (2), 2002. Frameless robotics has been compared with frame-based stereotaxy in the articles by Hang, Q. et al., “The application of the NeuroMate Robot: a quantitative comparison with frameless and frame-based surgical localization systems”, Computer Aided Surgery, Vol. 7 (2), 2002, pp 90-98; by Morgan, P. S. et al., “The application accuracy of the PathFinder neurosurgical robot”, Computer Aided Radiology and Surgery, CARS'2003, Elsevier 2003; and by P. S. Morgan, et al., “Improved accuracy of PathFinder Neurosurgical Robot”, International symposium on Computer Aided Surgery around the Head, CAS-H′2004, 2004.
In all cases, the desired Target Registration Error (TRE) is 1-2 mm, and is critically dependent, except for the interventional imaging systems, on the registration between the preoperative images and the intraoperative situation.
Referring again to Table 1, it is observed that existing support systems for precise targeting in minimally invasive keyhole neurosurgery system do not appear to provide a fully satisfactory solution for all such applications. Each of the methods has at least one characteristic which is significantly disadvantageous in comparison with the other methods, as shown by a single + sign. Thus, stereotactic frames entail patient morbidity, require head immobilization and manual adjustment of the frame, and do not allow intraoperative plan changes. Navigators are frameless but require line-of-sight between the position sensor and the tracked instruments and require time-consuming manual positioning of a mechanical guiding arm. Existing robotic systems can perform limited automatic targeting and mechanical guidance but are cumbersome, expensive and difficult to use, and require head immobilization. Interventional imaging systems do not incorporate preoperative planning, have limited availability, are time-consuming and incur high costs.
There therefore currently exists a need for an image-guided system for precise automatic targeting of structures inside the brain that is less disadvantageous overall than the prior art systems, and preferably combines the advantages of the stereotactic frame—accuracy, relative low cost, mechanical support—with the advantages of robotic systems—reduced patient morbidity, automatic positioning, intraoperative plan adaptation—and which has a small system size and does not mandate head immobilization.
The disclosures of each of the publications mentioned in this section and in other sections of the specification are hereby incorporated by reference, each in its entirety.